1. Field of the Invention
The present invention relates to a method for reudcing formation of nitrogen oxides during operation of burners for solid, liquid, and gaseous fuels, the fuel being injected into a combustion chamber through a fuel pipe, and combustion air being supplied to the combusion chamber around the fuel pipe and around a fuel nozzle at the end of the fuel pipe through a combustion air pipe that extends into in a flame pipe in the region of the fuel nozzle, with which method the exhaust gases are led through an exhaust conduit and a part of the exhaust gases is supplied from the exhaust conduit to the combustion chamber. Furthermore, the invention relates to a corresponding apparatus.
2. Description of the Prior Art
An increasing interest in the protection of the enviroment leads to a continuous tightening of requlations regarding the emission of pollustants from oil and gas burners. Particular attention is directed to the emission of nitrogen oxides (NO.sub.x). These contribute, inter alia, to the formation of acid rain and ozone. For example, primarily nitric oxide (NO) is responsible for the formation of ozone. The emission of nitrogen oxides is directly correlated to the height of the flame temperature. At elevated temperatures above 1200.degree., the air components nitrogen and oxygen react to NO.sub.x according to the so-called Zeldovich mechanism.
Based on this knowledge, exhaust gas feed-back systems are used to reduce pollutants. By doing so, on the one hand, and cooling of the flame is achieved, and, on the other hand, the partial pressure of oxygen is minimized by admixing inert exhaust gas, this partial pressure of oxygen being a prerequisite for the formation of NO.sub.x.
In commercially available burners, fuel is injected into the combustion chamber through a central aperture of a disk shaped stabilizer that operates as a baffle element and is also referred to as baffle disk. Combustion air is supplied before the stabilizer through a combustion air pipe around the the fuel supply. In the region of the stabilizer, this combustion air pipe extends into a flame pipe. The admixture of exhaust gas takes place behind the stabilizer--as seen from the fuel supply--by means of an adaptor that encompasses the combustion air supply in a collar-like manner. In order to improve effectiveness, the combustion chamber is often divided into complicated combustion zones which are separated by means of microprocessor controlled shutter mechanisms. Consequently, the present burners must be replaced by complicated and expensive burners when exhaust gas feed-back systems are installed. In this way, not only the changing over to a new system, but also its maintenance becomes complicated and expensive.